The present invention relates generally to pipeline fittings and has particular reference to gate valves adapted to shut off the flow of liquid in pipelines, made use of in diverse fields of industry, such as mining, construction, chemical, petroleum production, and the like.
The invention can find most utility when applied for pipelines laid in underground coal winning by the hydraulic method.
A large number of diverse types of gate valves are known for use currently which comprise substantially a housing hermetically joined with pipelines, and a closing member translationally traversable in between the sealing elements of the housing.
However, despite a great diversity of gate valves now in use the problem how to prolong their service life is yet far from being completely solved, especially when the gate valves are used to shut off the flow of liquids containing solid impurities, as the closing members and their sealing elements are liable to destruct within a short period of time. This is due largely to the fact that when the pipelines are shut off or intercommunicated, adverse conditions for the closing members and sealing elements arise, consisting in that a passageway is established when the pipelines are communicated to each other or shut off, said passageway being confined within the bottom end of the closing member, the gate valve housing and the sealing elements and featuring the same cross-sectional area at the entrance and exit thereof. We have been successful in finding out that the flow of liquid along such a passageway defines a void space situated beneath the closing member close to the entrance to the passageway, said void space considerably choking the free passage area and, consequently, reducing the hydrodynamic pressure in the flow, thus providing the conditions for the onset of cavitation. Before leaving the passageway the flow of liquid expands, the hydrodynamic pressure rises and the cavities are broken, all this leading to rapid failure of both the closing member and the sealing elements.